Function To Change the Parameters of DBR

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/* Function To Change the Parameters of DBR */

Recover_with_values()
{
int val =0;

/* Jump Code of 3 Bytes For Floppy */
b.code[0] = 0xEB;
b.code[1]= 0x3E;
b.code[2]= 0x90 ;

/* System Id of 8 Bytes */
strcpy(b.system_id, "+05PSIHC");

/* Bytes Per Sector = 512 */
b.bytes_per_sec = 512;

/* Sector per Cluster for 1.44M 3.5" Floppy = 1 */
b.sec_per_clus = 1;

/* Number of Reserved Sectors = 1 */
b.res_sec =1;

/* Number of FAT Copies = 2 */
b.fat_copies =2;
/* Number of Root Directory Entry = 224 */
b.root_dir_entry =224;

/* Number of Sectors on Disk = 2880 */
b.no_sects =2880;

/* Media Descriptor Byte For Floppy = F0 (H) */
b.format_id =0xF0;

/* Sectors Per FAT = 9 */
b.sec_per_fat =9;

/* Sectors Per Track = 18 */
b.sec_per_trk =18;

/* Number of Sides = 2 */
b.no_sides =2;

/* Number of Special Reserved Sectors (or Hidden
Sectors) = 0 */
b.no_sp_res_sect =0;

/* Use For Floppy Disk*/
val = abswrite ( 0, 1, 0, &b ) ;

if ( val == -1 )
{
printf ( "\n Disk Write Error...bad sector\n" ) ;
printf ( " Disk was not Recovered." ) ;
exit ( 1 ) ;
}

return 0;
}

display_info()
{
printf ( "\n Jump Code (Hex) = %X%X%X (H)\n",
b.code[0],b.code[1],b.code[2]);
printf ( " System ID = %s\n", b.system_id ) ;
printf ( " Bytes per sector = %d\n", b.bytes_per_sec ) ;

printf ( " Sectors per cluster = %d\n", b.sec_per_clus ) ;

printf ( " Reserved sectors = %d\n", b.res_sec ) ;

printf ( " FAT copies = %d\n", b.fat_copies ) ;

printf ( " Root directory entries = %d\n", b.root_dir_entry ) ;

printf ( " No. of sectors on disk = %u\n", b.no_sects ) ;

printf ( " Media Descriptor Byte = %X\n", b.format_id ) ;

printf ( " Sectors per FAT = %d\n", b.sec_per_fat ) ;

printf ( " Sectors per track = %d\n", b.sec_per_trk ) ;

printf ( " No. of sides = %d\n", b.no_sides ) ;

printf ( " No. of reserved sectors = %d\n", b.no_sp_res_sect ) ;
return 0;
}

Comments on coding:

The structure boot is used to access the DBR, to read-write the parameters of the disk. The function display_info(), displays the various parameters of the disk, reading from the DBR. The function Recover_with_values() is used to modify and recover the parameters of DBR of Floppy.

The values used by the function Recover_with_values(), are for parameters of 1.44MB, 3 ½ inch floppy disk’s DBR. The description of these values has been given in the table given next:

Value

Description

b.code[0] = 0xEB;
b.code[1] = 0x3E;
b.code[2] = 0x90 ;

Jump Code of 3 Bytes For specified Floppy, has been given EB 3E 90(H)

strcpy(b.system_id,"+05PSIHC");

System Id of 8 Bytes. It is calculated with current date and time of the system, however almost anything works.

b.bytes_per_sec = 512;

Bytes Per Sector = 512

b.sec_per_clus = 1

Number of Sectors per Cluster for 1.44M 3.5" Floppy is 1

b.res_sec = 1;

Number of Reserved Sectors = 1

b.fat_copies  =  2;

Number of FAT Copies = 2

b.root_dir_entry = 224;

Number of Root Directory Entries for the specified floppy disk = 224

b.no_sects  = 2880;

Number of Sectors on Disk = 2880

b.format_id = 0xF0;

Media Descriptor Byte For the specified Floppy = F0 (H)

b.sec_per_fat = 9;

Number of Sectors Per FAT = 9

b.sec_per_trk = 18;

Number of Sectors Per Track = 18

b.no_sides = 2;

Number of Sides = 2

b.no_sp_res_sect = 0;

Number of Special Reserved Sectors (or Hidden Sectors) = 0

 

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Data Recovery with & without Programming


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